This invention relates to a method measuring electric-field funneling length created by irradiating a semiconductor charge-collecting junction with an electron-hole-pair generating charged particle, and more particularly to where the charged particle penetrates beyond the depletion region in the semiconductor layer and yet all the charge generated at the selected energy level is collected by drift rather than diffusion.
One form of semiconductor charge-collecting junction, a silicon surface (Schottky) barrier detector, is used extensively for both counting and energy measurement of charged particles. For heavy ions with limited range in silicon, a partially depleted detector can knowingly be used to accurately measure the ion kinetic energy, provided that the ion range does not exceed the width of the depletion layer. However, it is not generally known that the range of the ion may actually exceed the depletion width and still have all of the charge generated by the ion collected at the Schottky barrier. This is due to an extension of the electric field outside the depletion region along the end of the ion track, an occurrence which has been labeled "field funneling," and is recognized in an article by C. M. Hsieh, P. C. Murley, and R. R. O'Brien, "Collection of Charge from Alpha-Particle Tracks in Silicon Devices," IEEE Transactions on Electron Devices, Vol. ED-30, No 6, pp. 686-693, June 1983.
In that article, the authors disclose collection time measurement apparatus in which a device under test is biased and irradiated with an alphaparticle source. The charge collected is then transmitted through an FET probe to a wide band amplifier and displayed on a high frequency oscilloscope. The collection time was measured through the FET probe. When an alpha-particle struck the collecting structure, the voltage began to drop rapidly as electrons were collected. The waveform was a negative voltage amplitude proportional to the collected charge. This waveform was amplified in a wide band amplifier and displayed on a high frequency real time oscilloscope. The pulse-heights were analyzed in a multichannel analyzer in a manner different from that employed in the present invention.